Conventional CAPTCHA (also interchangeably referred to as reverse Turing Test (RTT)) techniques principally rely on text being represented as images and optical character recognition (OCR) algorithms to convert the images back to text. However, these conventional CAPTCHA techniques are severely deficient in terms of being inconvenient, insensitive, unfair, inefficient, limited in the use of input/output (I/O) components and platforms, etc.